Draught marking is cause by many different issues as you can see in the photo above. This is called filtration soiling, Leave in black draught marking and is unsightly and a problem to remove. Only light coloured carpet will show the effects of draught marking. Some can be removed but not all, it depend on the time it been in your carpet and how bad it is and how many years it been there. But if it can be removed it can start to show again in weeks. This will come under specialist stain removal, and there is usual a separate charge to remove this. If you need any Free Advice call Deep Clean.